| 摘要 |
A drill bit (10) comprises a cast body (12) with full length wide overlapping integral spiral stabilizer lands (14) between intervening spiral grooves (16), integral short, strong, stubby spiral fingers (18) reinforced by additional web portions (12a) angularly spaced about a short core receiving bore (b) and the longitudinal axis of the body (21). An inclined core ejection passage (P) extends radially outwardly from a spherical inlet end thereof connected to the core receiving bore (b) and at which an inclined hard core cutter breaker inserted within a pocket is situated. The leading sides of the fingers have support surfaces (18a) and shoulders (18b) for supporting engagement with composite abrasive compact cutters comprised of a carbide backing (30a) bonded to the support surfaces (18a) and layers of bonded polycrystalline abrasive particles at opposite cutting sides (30b) inclined at a negative rake angle. The body is also provided with flushing fluid passages (24) and a central bore at its drive end adapted with means (22) to connect drive means, with a flushing fluid passage therein to drive the drill bit (10).
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